This invention relates to apparatus for dispensing quantities of liquefied gas having a boiling point below ambient temperature. It is particularly concerned with a method and apparatus for dispensing droplets of chosen or suitable volume of a cryogenic liquid, for example, liquid nitrogen.
Liquefied gases are typically used in industry in bulk quantities and can thus be metered by conventional methods. One some occasions, however, a need arises for only a small quantity, for example, up to a few milliliters, of liquefied gas to be delivered. Such a need may arise when bottling a beverage. It is often desirable for the neck of each bottle to contain an atmosphere consisting essentially of a gas such as nitrogen that does not adversely affect the quality of the beverage. Moreover, even if nitrogen is not required for this reason it has been found that in a closed plastics bottle containing a beverage a partial vacuum can be created in its neck as a result of a reduction in temperature, which partial vacuum can cause a wall of the bottle to be sucked inwards, and accordingly filling the neckspace with a small volume of nitrogen (or other suitable gas) before fitting a closure to the bottle will guard against the creation of such a partial vacuum. Another example of the need for an apparatus and method for delivering a small volume of liquefied gas such as liquid nitrogen is in the freezing of individual comestible items.
Previous attempts to solve the problem of delivering or dispensing small metered quantities of liquid nitrogen (or other liquefied gas) have involved employing a vertical delivery pipe having two valves in it. By opening the upper valve a chosen volume of liquefied gas may be trapped between the valves. The upper valve is then closed and the lower one opened. Thus, a chosen volume of liquefied gas can be dispensed.
Such an apparatus suffers from the drawback that liquefied gases such as liquid nitrogen having a boiling point (-196.degree. C.) well below ambient temperature, vaporise very readily, and that, in practice, it is difficult to avoid vaporisation of some of the liquid nitrogen between the valves from taking place before the liquid nitrogen can be dispensed. Moreover, in practice, the amount of vapour that is formed varies.